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Abstract
UNL-1, a lytic bacteriophage of Pseudomonas aeruginosa isolated at the University of Nebraska, possesses a novel DNA repair phenotype. Bacteriophage DNA repair is quantified by Weigle reactivation, an experimental method in which UV induced bacterial host cells are infected with UV-C irradiated virus and plaque forming units enumerated. Previously, Weigle reactivation has only been observed in P. aeruginosa when host cells containing UV resistance plasmid R-2 and a functional rec A gene are treated with UV-C radiation before bacteriophage infection. When UNL-1 is damaged with UV-C radiation to 1% infectivity, it is capable of over 10-fold reactivation when infecting P. aeruginosa host cells that have been previously exposed to UV-A radiation. However, the virus does not reactivate if P. aeruginosa is instead exposed to UV-C radiation. The reactivation is also not dependent upon a functional rec A gene or a UVR plasmid, as shown previously, supporting the hypothesis that this is a new DNA repair phenotype. UNL-1 Weigle reactivation has also been shown to be synergistic to photoreactivation, so when incubating the pour plates in the fight, a seventy-fold reactivation results. The gene or genes responsible have not yet been identified, but the activity seems to be dependent upon host excision repair and at least partially upon the rec 2 gene, which plays a role in rec A regulation. Although the exact nature of this repair is still unknown, this virus has been shown to reactivate if the host is first exposed to sunlight. It also shows some evidence of providing UV resistance to host cells when the bacteriophage is pseudolysogenic or in a semi-stable interaction with the cell. These interactions result in the production of brown pigment in 1–10% of the pseudolysogens. The phenotype changes in pseudolysogens containing UNL-1 could be important in understanding the survivability of some viruses in the environment and the interaction of bacteriophage with their host cells.
